Removed the top on the Pre Amp, the stock Electro Harmonix 6922 can't be pulled straight out as they are glued in place at one end, probably to reduce vibrations or from coming loose in transit. White silicon is applied to the PCB and Black to the valve. I found the easiest way of removing them, was to take off the side panels of the enclosure and just cut through the center of the silicon with a sharp knife. Once the valve was taken out it was easy to remove the remaining silicon from both parts.